Compliant pins are used to facilitate an electrical connection between, for example, printed circuit boards and associated circuitry. In the typical pin connector system, upon insertion of a compliant pin into a complementary circuit board aperture, a portion of the pin mechanically engages with the electrically-conductive sidewall of the aperture to achieve and maintain a positive electrical connection therewith. It is desirable that the compliant pin effect resilient engagement with the aperture so that contact pressure is maintained while ensuring that such pins may be inserted into the circuit board in a high density array without requiring excessive installation force. Stated in another manner, the resilient flexing of the mounting portion of a compliant pin most preferably provides a pin retention force that is equal to or only slightly less than the insertion force required for pin installation.
It is to be emphasized that the mechanical engagement between the pin and aperture sidewall must be of a non-destructive nature in order to avoid damage to either the pin or aperture sidewall which would tend to severely limit connector system performance and integrity. By way of example, it is noted that Military Specification MIL-C-28,859 requires that the aperture withstand repeated pin installation and removal with only minimal sidewall deformation.
Additionally, the mechanical engagement between the pin and aperture must be such that the installed pin is capable of resisting applications of torque thereto as may occur, for example, when making wire-wrap connections to an exposed end of the pin subsequent to its installation in the circuit board. Indeed, it will be appreciated that a small measure of torsional loading on the pin inevitably occurs during its installation or removal. Torsional resistance is further required in order to maintain the proper alignment between the pin and circuit board and to preclude an electrical short circuit between adjacent pins. Most preferably, torsional loads are absorbed by the resilient flexing of the mounting portion of the compliant pin itself, thereby avoiding the scoring and/or wholesale destruction of opposed pin connector and aperture sidewall contact surfaces which would otherwise result from relative rotation therebetween.
Another difficulty encountered in pin connector systems is the formation of oxides and other surface films on the exposed contact surfaces of both the pin connector and the aperture sidewall prior to the mechanical engagement therebetween. The films, which in large part survive the axial contact wiping generated between the pin and aperture during pin installation, ultimately reduce the quality of the electrical connection achieved by known connector systems. It is therefore desirable to promote circumferential, as well as axial, contact wiping of the aperture sidewall with the individual beams of the pin connector mounting portion during connector system assembly.
Known pin connectors generally utilize a split wall or twin beams that are radially contractable upon insertion of the pin into an aperture thereby to provide a positive electrical and mechanical connection to the circuit board. An example of a compliant pin heretofore known and used is found in U.S. Pat. No. Re. 29,513 reissued Jan. 10, 1978, to Johnson. It is noted that such known "needle-eye" configurations also include compliant pins having three beams which are equi-spaced about the connector periphery, as taught in U.S. Pat. No. 3,545,080 issued Dec. 8, 1970, to Evans.
The problem with pins of conventional needle-eye design is that, in order to meet the force requirements incident to insertion, retention and torque, such known pins are relatively stiff. As a result, a large insertion force is typically required, and the aperture in the printed circuit board often complies more than the pin. This results in significant hole deformation, both electrical and mechanical damage to the circuit board, and ultimate compromise of the integrity of the electrical circuit. Such deformation of the aperture additionally limits the resilient retention force achievable by the pin while encouraging additional aperture damage upon the torsional loading of the pin.
The prior art further teaches pin connectors having a mounting portion comprising three beams disposed in a triangular array wherein the first beam extends lengthwise in cross-section radially away from the central longitudinal axis of the pin and the second and third beams, offset from said longitudinal axis, extend in cross-section laterally away from the first beam, as described in U.S. Pat. No. 3,997,237 issued Dec. 14, 1976 to White. However, such pins fail to provide sufficient retention force and reusability, as pin installation is characterized by the relative sliding and subsequent jamming together of the beams thereof, whereby little resilient radial biasing of the beams is available for pin connector retention and the achievement of a positive electrical contact. Indeed, it is noted that the patent to White is directed to supplying solder into the aperture subsequent to pin installation, whereafter the pin is soldered into place in order to provide both sufficient pin retention force and positive electrical contact.
Still further, severe deformation of the aperture itself is likely to occur upon insertion of the White pin therein, in as much as the beams are essentially wedged into the aperture. And, subsequent to its installation, the beam configuration taught by White is unable to resist torque in a non-destructive manner, as it provides no compliance within the mounting portion of the pin itself to prevent the beams from gouging the aperture sidewall.